TETRANDRIA. TETRAGYNIA, HT 
166. POTAMOGETON, L, (Pond-weed.) 
Calia 4-leaved. Corolla 0. Style 0. Seeds 4, 
Leaves sheathing, those of the stem often alternate, flo. 
ral leaves mostly opposite; flowers spiked, terminal or 
axillary; ramuli and spikes baving frequently 2 sheathes 
; at the base. Nut 1-seeded, cochieate; embryon erect, 
exalbuminous, curved or involute. : 
Species. 1. P.natans. 2. fuitans. 3. heterophyllum. 4. 
setaceum. 3. perfoliatum. 6. lucens. 7. crispum. 8. grami- 
neum. 9. pectinatum.~-A genus of aquatic plants, appa- 
rently confined to Europe and North America; those of 
the latter continent at the same time common also to Eu-~ 
‘ Tope, 
167. RUPPIA. L. (Tassel Pond-weed.) 
Caliz none. Corolla none. Seeds 4, pedicel- 
late, . 
A maritime aquatic plant with capillary branches; leaves 
~  gramineous, sheathing; on the stem alternate, towards the 
_ flower nearly opposite; flowers in a spikelet or spad:x, so- _ 
litary, mostly terminal, distichal, peduncle convolute, 
stretching or contracting according to the depth of water, __ 
after the manner of Vuisneria; *“calix 2-valved, decidu- 
ous,” Jusstev. Fruit subulate, when mature incurved at 
the point. Nut gibbous, containing one seed; embryon 
erect, attached (as in many other plants of the same natu- — 
ral class,) to a germinal body apparently of the nature of 
the root.t 
- Species. 1. R. maritima. Common probably to every 
part of the world. ‘ 
+ Being distinct from the ordinary cotyledons, albumen or 
perisperm, to distingish it from them I propose the name of — 
somarhize, (somarhiza) or a radical inactive body affording a 
temporary nourishment to the embryon with which it possesses _ 
a simple vascular connection, but without producing any spe- 
cies of radicles or legves, often in the form of a cohering cal- 
lous tubercle, it exists longer than ordinary cotyledons, and dif- 
fers from an extraneous perisperm in its vascular connection 
= With the embryon. 
eo 
